The goal of crop breeding is to combine various desirable traits in a single variety/hybrid. Such desirable traits may include greater yield, resistance to insects or pests, tolerance to heat and drought, better agronomic quality, higher nutritional value, growth rate and fruit or pod properties.
Breeding techniques take advantage of a plant's method of pollination. There are two general methods of pollination: a plant self-pollinates if pollen from one flower is transferred to the same or another flower of the same plant or plant variety. A plant cross-pollinates if pollen comes to it from a flower of a different plant variety.
Plants that have been self-pollinated and selected for type over many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny, a homozygous plant. A cross between two such homozygous plants of different varieties produces a uniform population of hybrid plants that are heterozygous for many gene loci. Conversely, a cross of two plants each heterozygous at a number of loci produces a population of hybrid plants that differ genetically and are not uniform. The resulting non-uniformity makes performance unpredictable.
The development of uniform varieties requires the development of homozygous inbred plants, the crossing of these inbred plants, and the evaluation of the crosses. Pedigree breeding and recurrent selection are examples of breeding methods that have been used to develop inbred plants from breeding populations. Those breeding methods combine the genetic backgrounds from two or more plants or various other broad-based sources into breeding pools from which new lines are developed by selfing and selection of desired phenotypes. The new lines are evaluated to determine which of those have commercial potential.
One crop species which has been subject to such breeding programs and is of particular value is dry bean (Phaseolus vulgaris (dry)). Beans are annual, warm-season legumes. Dry beans are generally harvested as mature dry seeds, as opposed to snap beans (also known as green beans, garden beans, or pole beans) which are generally harvested when the seeds are succulent. The bean leaf is occasionally used as a leaf vegetable, and the straw is used for fodder. Some common varieties of dry bean include great northern, navy, kidney, and pinto.
The dry bean is a diploid (2n=2x=22) plant. Genetic improvement of dry bean has been achieved largely through the selection of varieties by applying conventional breeding techniques of self-pollinated crops. While breeding efforts to date have provided a number of useful dry bean lines with beneficial traits, there remains a great need in the art for new lines with further improved traits. Such plants would benefit farmers and consumers alike by improving crop yields and/or quality.